PLC Modeling the Scan Cycle
The first criterion is to extent the scan cycles are modeled. Usually, a program on a PLC is executed cyclically. However when doing only static program analysis the cyclical execution is not interest: models have to take only a single execution of program into account. The most realistic way of modeling PLC is to build the cyclical execution into the model equipped with some real-time information about the duration of each cycle. In some cases, the precise duration of a scan cycle is not of interest, but the cyclic behavior is. Finally when the environment is much slower than the scan cycle length we can use models where program execution is instantaneously. PLCs are embedded systems, and correctness of such system concerns the interaction between a controller and its environment. Therefore, a composition of two models has to be analyzed: one models the PLC with its program and one models the environment. The different ways of modeling scan cycles characterize the abstraction levels on which environment and PLC are composed.
Models without scan cycle
Program models that do not consider the scan cycle are intended mainly for static program analysis. They are not composed together with an environmental model. The models typically do not include real time. The properties that can be investigated based on such models are e.g. data independence between parallel components, unreachable code, safe structure of programs, etc. it can be checked whether a program conforms to some programming guidelines. It is reasonable to restrict formal analysis only to well constructed program, e.g. not every syntactically correct program, but programs using a certain programming discipline.
Models with explicit scan cycle
Generally, for each program execution there are a lower and an upper time bound. The lower time bound results from the time needed for update an output and input and the self checks of the operation system. The upper time bound depends on the longest execution path in the program. Under the assumptions it is important that we don’t consider interrupts, they make it difficult to predict a scan cycle duration.
Posted by Cartiman Iman
♥ Favorite Labels ♥
- ► 2015 (130)
- ► 2014 (15)
- ► 2012 (274)
- Low End PLC of Diamond Control System
- Internal Block of SERCOS IF Module
- Data Block and Timer Functions of Simatic S7
- Single PLC of SERCOS FA-M3
- High End PLC on Siemens S7
- Programmable Logic Controller on Diamond
- Full Size Operator Interface of L2000 PLC
- L2000 Programmable Logic Controller
- Adding Timers to PLC Programming Language
- PLC Programming of Timing Aspects
- Improving PLC programs Verification Using Abstract...
- MicroSmart All in One Type CPU of PLC
- PLCTOOLS Graph Transformation for PLC Design
- The Function Block Diagram EDITOR of Hosts PLCTOOL...
- Translational Semantics of Ladder Diagram through ...
- The Steps Approach in Implementing PLC Programs
- PLC of Instruction List Tools Available Resulting ...
- PLCs, Ladder Diagram and Validation Issue
- PLC Models with Implicit Scan Cycle
- PLC Modeling the Scan Cycle
- Getting Started with the PLC_DIAL
- The Connection PLC and PLC_DIAL over Telephone Lin...
- The Conclusion of Evaluation SCADA in Trans Power
- Reliability Electric Utility SCADA System
- IEEE RTS SCADA Systems
- The Construction and Analysis of IEEE RTS of SCADA...
- Motorola Communications for SCADA Solutions
- The Limitations of SCADA System over GPRS
- GPRS Communications for SCADA
- SCADA Operate over GPRS Network
- PLC and Sensor Constraint in Water Irrigation Cont...
- PLC based Canal Automation Components
- Canal Automation History
- PLC Implementation in Canal Automation Work
- Adaptability and Integration of SCADA Wireless Net...
- The Evolution of Wireless SCADA
- Communication Technologies in Building Automation
- Control Systems in Building Automation
- Middleware Software Components of Industry Automat...
- Real Time Industrial Automation
- Open Development Kit for Integrating Special Tasks...
- WinAC Open Development Kit Interfaces
- WinAC Slot PLC Increased Operational Reliability
- Software PLC WinAC Basis and PLC WinAC RTX
- PC based Control System with Simatic WinAC
- Utilization of Simatic Know-How
- Simatic WinAC PLC in the PC
- Manual Control and Automatic Control for Frequency...
- Smaller HMI Hardware for Tight Spaces
- Integrated Automation System Totally Integrated Au...
- Totally Integrated Automation Democase
- Weighing Machine Using PLC
- SCADA Security Implementation in a Plant
- Weighing Machine Using PLC Omron
- SCADA System Administrative Aspects
- SCADA Communication and DNP3 Protocol
- Users Tout PLC Size and Usability
- Increase the Efficiency of Sortation and AS/RS Mac...
- The Automation System Using Electrical CAD Softwar...
- The Hybrid PLC Modules
- PLC Course to Overcome Industry Demands
- Hybrid PLC: PLC Connected to PC
- Commercially Available System PLC Training
- The 2201 Monitoring System by Bently Nevada and Al...
- The 2201 Monitoring System with PLC 5 Controller
- ▼ January 2011 (65)
- ► 2010 (447)